Field of Invention
The present invention relates to a radio frequency interference suppression technology. More particularly, the present invention relates to a radio frequency interference suppression circuit.
Description of Related Art
Along with the development of the modern technologies, the number and the type of the electronic equipments increase. Not only the electric power is consumed greatly, but also the unnecessary electro-magnetic energy increases. The energy affects the normal operation of the other equipments or systems. Under such a complex electro-magnetic environment, how to suppress the electro-magnetic interference therebetween to make the equipments and systems operate normally is a critical problem to be solved. An era of high frequency, high power density and high efficiency of the power electronic devices is arrived due to the application in high frequency band of the new power field effect components. The power conversion process of these power electronic devices results in larger current or voltage pulses that cause serious electro-magnetic interference. Such interference forms the radio frequency interference (RFI) after a near field electric coupling or a far field electric coupling to greatly affect the electro-magnetic environment and the power system.
The transmission and the delivering of the RFI is formed by the following components: a differential mode interference source, a noise transmission and coupling path and an antenna. The differential mode interference source mainly refers to the inrush current or voltage generated during the turn-on and turn-off of the semiconductor elements within the electronic equipment. The inrush current or voltage signal is the original differential mode interference source. Combining with the transmission path, there are various current driving mechanisms described below.
Reference now is made to FIG. 17. FIG. 17 is a diagram of an equivalent delivering model of the differential mode loop. The current-type excitation mechanism is described below. At first, the interference signal is generated by the differential mode interference source V_dm. The common mode interference signal V_cm is further generated at the parasitic impedance L_return of the high frequency differential return path by transmitting the interference signal through the differential mode loop that includes impedances L_signal, L_return and R. Such a high frequency voltage signal acts as an excitation source between the input and output wires. A common mode current I_cm is formed by passing the high frequency voltage signal through the loops such as the parasitic capacitor C_ant between the input and output wires and the ground. Accordingly, the wires form an effective dipole antenna that the electronic equipments generate RFI therethrough.
                    {                                                                              I_cm                  ~                  j                                ⁢                                                                  ⁢                                  ω                  ·                  C_ant                  ·                  V_cm                                                                                                                          V_cm                  ~                  j                                ⁢                                                                  ⁢                                  ω                  ·                  L_return                  ·                  I_dm                                                                                                        I_dm                ≈                                  V_dm                  /                  R                                                                                        (                  Equation          ⁢                                          ⁢          1                )                                          I_cm          ~                      -                          ω              2                                      ·                  C          ant                ·        L_return        ·                  V_dm          /          R                                    (                  Equation          ⁢                                          ⁢          2                )            
According to equation 1 and equation 2, the common mode current generated in the current-type excitation mechanism is directly proportional to the impedance of the inner differential mode current return path of the electronic equipments and is directly proportional to the square of the frequency and the amplitude of the differential mode interference source.
Accordingly, what is needed is a radio frequency interference suppression circuit to address the above issues.